1. Field of the Invention
The invention relates to a thermal spray method for the manufacture of a heat insulating coat and to machine components with a heat insulating coat of this kind; it furthermore relates to uses of machine components of this kind.
2. Description of the Prior Art
A method for the manufacture of a plasma spray coat is known from DE-C 23 28 395 in which zirconium silicate ZrSiO.sub.4 (or ZrO.sub.2.SiO.sub.2) is sprayed on. This material, which is very heat resistant ("fireproof") occurs naturally as a raw material, namely as sand from the mineral zircon. In the disclosed method a spray coat arises which is substantially composed of a mixture of tetragonal stable zirconium oxide ZrO.sub.2 and amorphous silicon dioxide SiO.sub.2. The tetragonal modification of the zirconium oxide is well suited for the development of protective coatings in contrast to the monoclinic modification, which is normally present at ambient temperature. These coatings form a protection against corrosion and wear at high temperatures.
Furthermore, it is known to use ZrO.sub.2 for the manufacture of heat insulating coats, for example as a coating of guide blades in gas turbines. The object of the present invention is to use a thermal spray method in such a manner that a heat insulating coat of zircon which is more economical than ZrO.sub.2, can be produced. In this it is to be achieved by suitable measures that the heat conductivity of a heat insulating coat of this kind is better up to 900.degree. C. than that of the known coatings of ZrO.sub.2 (heat conductivity index about 0.6-1.0 W/m.K at atmospheric pressure and room temperature).